Vulnerability to climate change (1): lake fish

Posted on June 6, 2011

Current climate change models suggest that over the next hundred years temperate zones will experience a higher frequency of extremely hot periods and an average temperature rise of 3-5 oC.   Organisms living in shallow lakes will be particularly vulnerable to these changes because of the lack of cool deep-water refuges and because increases in water temperature raise the respiratory demand for soluble oxygen but lower its availability.  Additions of nutrients, for example those in agricultural runoff, aggravate the problem by stimulating the growth of plants.  This increases shading, which reduces photosynthesis and the release of oxygen.  To examine the possible interactive effects of climatic warming and nutrient enhancement, English ecologists maintained separate populations of three-spined stickleback, a common European fish with a high tolerance for temperature variation and nutrient loading, under various combinations of temperature (ambient; ambient + 4oC) and fertiliser (none;  300 µg/L, N:P = 5:1; 3000 µg/L, N:P = 50:1).  The experiment made use of 24  2 m diameter outdoor tanks furnished with organic sediment and inoculated with local pond plankton.  After 16 months, fish abundances had dropped dramatically and were entirely extinct  in the tanks where temperatures and nutrient loading had both been raised.  The main reason for these declines appeared to be oxygen deficiency: in the warmed tanks dissolved oxygen levels were consistently low and fell below 5mg/L for more than half of the year.  Warming shifted the timing of peak abundance of zooplankton prey back by around a month but didn’t affect the timing of the stickleback breeding season, which showed that warming has the capacity to reduce stickleback recruitment by creating a mismatch between periods of spawning and maximum  food availability.  These findings suggest that an increased frequency of warmer years will mean a precarious future for lake fish, especially the many species with lower environmental tolerances than sticklebacks.  

Reference:  Moran, R. et. al.  2010.  Influence of simulated climate change and eutrophication on three-spined stickleback populations: a large scale mesocosm experiment.  Freshwater Biology 55, 315–325.